It is well known that oil and gas wells pass through a number of zones other than the particular oil and/or gas zones of interest. Some of these zones may be water producing. It is desirable to prevent water from such zones from being produced with produced oil or gas. Similarly, it may be desirable to shut off gas flow from an oil-producing well, or vice versa. Where multiple oil and/or gas zones are penetrated by the same borehole, it is desirable to isolate the zones to allow separate control of production from each zone for most efficient production. External packers have been used to provide annular seals or barriers between production tubing and well casing to isolate various zones.
It has become more common to use open hole completions in oil and gas wells. In these wells, standard casing is cemented only into upper portions of the well, but not through the producing zones. A tubing assembly or string is then run from the bottom of the cased portion of the well down through the various production zones. As noted above, some of these zones may be zones producing undesired fluids, such as, for example, water zones, which must be isolated from any desirable produced fluids. The various production zones often have different natural pressures and must be isolated from each other to prevent flow between zones and to allow production from the low pressure zones or from only selected zones.
Open hole completions are particularly useful in slant hole wells. In these wells, the wellbore may be deviated and run horizontally for thousands of feet through a producing zone. It is often desirable to provide annular barriers along the length of the horizontal production tubing to allow selective production from, or isolation of, various portions of the producing zone.
In open hole completions, various steps are usually taken to prevent collapse of the borehole wall or flow of sand from the formation into the production tubing. Use of gravel packing and sand screens are common ways of protecting against collapse and sand flow. More modern techniques include the use of expandable solid or perforated tubing and/or expandable sand screens. These types of tubular elements may be run into uncased boreholes and expanded after they are in position. Expansion may be by use of known methods in the art, including for example, inflatable bladders, use of an expansion cone, swellable material expansion, etc., in the tubular members. However, in many cases, due to irregularities in the borehole wall or simply unconsolidated formations, expanded tubing and screens will not prevent annular flow in the borehole. For this reason, annular barriers as discussed above are typically needed to significantly reduce or stop annular flow, even against significant differential pressure, in the borehole.
Use of conventional external casing packers for such open hole completions presents a number of problems. They are significantly less reliable than internal casing packers, they may require an additional trip to set a plug for cement diversion into the packer.
Efforts have been made to form annular barriers in open hole completions by placing a rubber sleeve on expandable tubing and screens and then expanding the tubing to press the rubber sleeve into contact with the borehole wall. These efforts have had limited success due primarily to the variable and unknown actual borehole shape and diameter. The thickness of the sleeve must be limited since it adds to the overall tubing diameter, which must be limited to allow the tubing to be run into the borehole. The maximum size must also be limited to allow tubing to be expanded in a nominal or even undersized borehole. In washed out or oversized boreholes, normal tubing expansion is not likely to expand the rubber sleeve enough to contact the borehole wall and form a seal. To form an annular seal or barrier in variable sized boreholes, adjustable or variable expansion tools have been used with some success. However it is difficult to achieve significant stress in the rubber with such variable tools and this type of expansion produces an inner surface of the tubing which follows the shape of the borehole and is not of substantially constant diameter.
In light of these difficulties, advancements in methods and apparatus for forming annular barriers in an open borehole are discussed in U.S. Pat. No. 6,854,522 to Brezinski, et al., entitled ANNULAR BARRIERS FOR EXPANDABLE TUBULARS IN WELLBORES, issued Feb. 15, 2005, which is incorporated herein by reference for all purposes.
Use of expandable tubing is not always desired or possible, however. Consequently, a method and apparatus for forming annular barriers in open hole boreholes without use of expandable tubing is desirable. It is desirable to provide equipment and methods for installing annular barriers in open boreholes, particularly horizontal boreholes, which provide a seal between production tubing and the wall of open boreholes.